(1) Field of the Invention
The invention relates to vacuum technology, and more particularly it relates to an apparatus for applying film coatings onto substrates in vacuum by ion-plasma sputtering.
The invention can be implemented in vacuum ion-plasma sputtering technologies, e.g. application of coatings, etching, surface-hardening, fusing of materials (conductive, resistive, dielectric) in the manufacture of articles with complex coatings of diverse compositions. Articles treated in the disclosed apparatus for application of film coatings can be broadly utilized in electronic, engineering and metallurgical industries, and in optics.
(2) Description of the Related Art
When film coatings are applied onto articles in vacuum by ion-plasma sputtering processes, of essential importance for ensuring high quality and efficiency of the process are the use of a pure inert gas (e.g. argon) containing no impurities, as well as providing of broad capabilities for controlling the quantitative composition of the working gases and for boosted pumping-out of gases from the working chamber, i.e. the chamber where the actual sputtering operation is performed. All these essential features are dependent on the structure of the apparatus for applying film coatings.
There is known an apparatus for applying film coatings onto substrates in vacuum, which is a part of the Z-600 Unit for ion-plasma sputtering of thin films (B. Heinz, Leybold-Heraeus GmbH, Hanau, BRD "Technology of Magnetron Sputtering for Producing Thin Films for Electronic Industry"). The apparatus comprises a vacuum working chamber with a holder of substrates and at least one unit for magnetron sputtering of materials, an evacuation chamber with either a diffusion pump or a turbo-molecular pump, connected with the working chamber via a control valve, and a pre-evacuation pump communicating with the working chamber via a conduit including a control valve.
When this apparatus is operated for applying film coatings, the sputtering process involves the use of argon containing admixtures of active gases adversely effecting the quality of the coatings obtained (e.g. their adhesion, their chemical composition, etc.), eventually causing rejects and thus reducing the productivity. The operation of the apparatus is further characterized by inadequate stability of concentrations of the working gases; as either the diffusion pump or the turbo-molecular pump employed is capable of pumping out all the gases present (argon included). This, in its turn is liable to affect the parameters of the plasma generation process, the sputtering rate and chemical composition of the film coating, thus likewise causing rejects and reducing the productivity. Boosted pumping out of the gases from the working chamber in the course of the sputtering process might also cause defective film coatings on account of inadequate stability of the parameters of the plasma generation process.
There is further known an apparatus for applying film coating onto substrates in vacuum (U.S. Pat. No. 4,606,929), comprising a working chamber with a holder of substrates and at least one unit for magnetron sputtering of materials, an evacuation chamber connected with the working chamber via a control valve, provided with a magnetron pump and communicating via a first conduit including a control valve with a gas source, and a pre-evacuation pump having its working space communicating with the working chamber via a second conduit.
When this apparatus of the prior art is operated for reactive sputtering processes (which take a relatively long time and are critical from the view point of the chemical composition of the film coatings produced), and it is necessary to add some more argon to support the required process parameters (as argon pressure is liable to drop in the course of the sputtering operation), commercially available argon is employed, more often than not which contain active gases affecting the required chemical composition of the film coatings and their adhesion to the substrates. Thus, with argon added to the working chamber, some time is required for pumping out the active gases introduced by this argon replenishment by the magnetron pump, while chemical processes that are liable to develop in the plasma over this period of time are capable of causing defects in the film coatings obtained. Thus, the coatings obtained have to be subjected to additional tests and checks to introduce appropriate corrections into the successive photo-lithographic processes. Furthermore, it should be pointed out that the apparatus of the prior art involves complications in conducting reactive sputtering processes also on account of the fact that the valve it utilizes for controlling communication of the working chamber with the evacuation chamber is operable in two positions only, i.e. the "open" and "closed" positions. This hinders the maintenance of the required quantitative composition of the working gases, as the magnetron pump would pump out the working gases always at the maximum rate affecting the total pressure of the gases in the working chamber, which calls for frequent corrections of this pressure.
The apparatus of the prior art has no provisions for boosted pumping out of the active gases from the working chamber, as the magnetron pump it incorporates offers a fixed pumping-out rate. The apparatus is not operable during the periods of maintenance of either the magnetron pump or the pre-evacuation pump, and its time of preparation for the sputtering process is prolonged.